We propose to examine the effects of executive control and fatigue on the maintenance of mobility and risk of mobility disability in older adults and their underlying brain substrates. Our overall working hypothesis is that mobility, executive control, and fatigue are closely linked through the frontal cortex-basal ganglia system in older adults. We propose to recruit 450 non- demented community-residing individuals age 70 years and older for baseline and annual follow-ups over the 5-year study period. Study measures will be administered in each yearly evaluation to identify cross-sectional and longitudinal effects of executive control and fatigue on mobility (aim 1). Functional Near Infrared Spectroscopy (FNIRS) will be used in each study visit to identify in motion PFC functional correlates of mobility (aim 2). Structural and functional MRI will be administered to a subsample (n=70) at baseline to augment our assessment of brain correlates of mobility.